The DLT8000 default block size

[Kevin Lawler_1]

Recently I have attached an external DLT8000 tape drive to an HP 9000 K class server running HPUX 10.20. We would like to use it to backup our Informix DB using OnTape. I have been unable to determine what the maximum block size is supported by DLT8000. Specifically what to set the TAPEBLK parameter in the "onconfig" file. We are using SAP 4.6b and Informix 7.31. Any help would be appreciated.
Thank you,
Kevin.

[Steve Lewis · Accepted solution]

I have done lots of testing with different block sizes. The informix default of 16 results in a slow backup. Increasing the block size to 32,64, or 128 gradually improves the overall speed but I found that over 128 the overall time to run ontape reduces again. The server I did the testing on wasn't exclusively mine so this may not be the case with everybody. I recommend 128. This also applies to DLT7000, 4000 and DDS drives.

[Stefan Farrelly]

There is no built-in block size on the DLT8000 unit itself. Its all dependant on the software app talking to it.

128 is the recommended optimal block size for fbackup. We use it on ours all the time.